(This story is part of a series, "The Uncounted: The deadly
epidemic America is ignoring")
By Ryan McNeill
ATLANTA, Ga., Sept 7 In 2013, the U.S. Centers
for Disease Control and Prevention released estimates of how
many people in the country die every year from antibiotic
resistant infections: 23,000. The agency estimates that an
additional 15,000 die annually from Clostridium difficile, an
infection linked to long-term antibiotic use.
The estimates, the agency said at the time, provided the
"first snapshot of the burden and threats posed by
antibiotic-resistant germs having the most impact on human
Since then, the estimates have been cited by untold numbers
of media outlets and scholarly reports. A Google search for the
estimates can yield nearly 100,000 hits. Reuters took a close
look at how the agency arrived at its numbers and made a
surprising discovery: They are based on so little hard data that
they could be off by more than 30 percent - more than 10,000
people - in either direction.
The statistical uncertainty is a byproduct of the nation's
lack of a unified surveillance system. No one at the state or
federal level knows how many people are dying from
Absent hard numbers, the agency turned to studies that rely
on statistical sampling, whereby a subset of the population is
studied and the results are extrapolated to cover the entire
Statistical sampling is common. Precision depends on the
size of the sample. The larger the sample, the greater the
precision. Reuters found that the CDC estimates are undermined
by small sample sizes, old data and information from a few
For example, the CDC estimate of 15,000 deaths annually from
C. difficile was based on monitoring of 88 inpatient and 33
outpatient laboratories in 10 areas across the country in 2011.
The 10 areas, part of the agency's Emerging Infections
Program (EIP), represented about 3.6 percent of the nation's
population at the time. Under the EIP, a handful of states are
given federal dollars to closely monitor infectious diseases,
generally in a few counties. They do not include population
centers like New York City, Southern California, Chicago or
Boston, or any locations in Texas or Florida.
Infectious diseases can occur at substantially different
rates in different areas. For example, the study on which the
estimates are based, titled "Burden of Clostridium difficile
Infection in the United States" and published last year in the
New England Journal of Medicine, found that the incidence of
hospital-acquired C. difficile was 47.3 per 100,000 people in
Klamath County, Oregon, while it was 159.1 per 100,000 in New
Because of statistical uncertainty, the estimate of deaths
from C. difficile could be anywhere from 7,600 to 20,000,
In many components of the CDC estimates, the agency relied
on even less information. One example is the deadly
carbapenem-resistant Enterobacteriaceae (CRE), which public
health officials describe as a nightmare bug with high
Not a single actual CRE death went into the estimates.
Instead, for CRE and five other infections, the agency
turned to a study in which researchers surveyed 183 hospitals
within the EIP program. The survey identified 504
hospital-acquired infections during a single year, 2011.
Based on those 504 infections, researchers extrapolated that
there were 721,800 such infections nationally. But because of
the small sample size, the estimate could be anywhere from
214,700 to 1.4 million.
CDC researchers then used the study, "Multistate
Point-Prevalence Survey of Health Care-Associated Infections,"
published in the New England Journal of Medicine, to estimate
how many of the 721,800 infections were Klebsiella species or
Escherichia coli, two of the more common types of bacteria that
can become resistant to the carbapenem class of antibiotics.
Then the CDC used data reported by about 2,000 hospitals to
its National Hospital Safety Network during 2009-2010 to
determine what percentage of the infections were drug-resistant.
The agency estimated 6.5 percent of people with those
drug-resistant infections die, based on a single study of a
Chicago teaching hospital in 2000 in which 34 people died.
Applying that percentage, they came up with their estimate of
600 deaths annually from CRE. Reuters found that using the CDC's
methodology, it could be twice that - 1,200 - or as few as 180.
(Edited by John Blanton)